Dermatological picosecond laser treatment systems and methods using optical parametric oscillator

ABSTRACT

Dermatological systems and methods for providing picosecond laser pulses at a plurality of treatment wavelengths, wherein at least one of the wavelengths is provided by an optical parametric oscillator (OPO) capable of providing picosecond laser pulses at a wavelength for treating one or more target tissue types such as a sebaceous gland, sebum, or collagen. In some embodiments, multiple OPOs may be provided to enable a wide range of selectable treatment wavelengths.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofpriority to U.S. patent application Ser. No. 15/820,421, filed Nov. 21,2017, entitled “Dermatological Picosecond Laser Treatment Systems andMethods Using Optical Parametric Oscillator,” which is incorporated byreference herein in its entirety. This application also claims thebenefit of priority to U.S. Provisional Application Ser. No. 62/851,615,filed May 22, 2019, having the same title and also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of electromagnetic-basedmedical treatment systems, and more specifically to systems and methodsfor treatment of dermatological conditions with lasers having at leastone wavelength determined by an optical parametric oscillator.

A variety of dermatological conditions are treatable usingelectromagnetic radiation (EMR). Sources of EMR for such treatmentsinclude lasers, flashlamps, and RF sources, each of which has distinctadvantage and disadvantage profiles. EMR devices have been used, forexample, treating abnormal pigmentation conditions, body sculpting(e.g., removal of subcutaneous adipose tissue), hair removal, treatmentof vascular skin conditions (e.g., spider veins), reduction of wrinklesand fine lines, and dyschromia, among other conditions. Abnormalpigmentation conditions may include tattoos and benign pigmented lesionsassociated with high local concentrations of melanin in the skin, suchas freckles, age spots, birthmarks, lentigines, and nevi, among otherpigmentation conditions. Both pulsed and continuous-wave (CW) lasersystems have been used to treat pigmentation conditions, although pulsedlasers are more frequently used.

Most applications of EMR in medical fields use a laser tophoto-thermally damage a target tissue while preserving surrounding oradjacent tissues or structures, thereby inducing a healing response inthe damaged tissue. The principle of selective photothermolysis, firstestablished in the early 1980s by Anderson and Parrish, was an importantdiscovery that led to the development of a variety of laser applicationsas standard of care in many medical fields such as ophthalmology anddermatology. Selective photothermolysis involves thermally damaging atarget tissue to promote a healing response. Ideally, the damage ishighly localized to only the particular target tissue (e.g., aparticular skin layer, or particular structures such as chromophoreswithin a skin layer), with surrounding non-targeted tissues/structuresremaining unaffected and thus available to facilitate the healingresponse in the targeted tissue.

As articulated by Anderson and Parrish, photothermolysis can be achievedwhen three conditions are met: 1) the wavelength of the laser is choseto have maximum absorption in the target tissue and minimal absorptionin non-targeted or surrounding tissue; 2) the pulse duration of thelaser should be equal to or less than (=<) the thermal relation time(TRT) of the target tissue; and 3) the laser fluence (i.e., energy perunit area) must be sufficient to exceed the thermal damage threshold ofthe target tissue. Together, these principles permit laser systems to bedeveloped that deliver energy at specific wavelengths, pulse durations,and fluences that are precisely controlled energy to damage targettissue while leaving non-targeted surrounding tissues and structuresunaffected.

Another key to medical laser system development has been the concurrentadvancement of laser technology. Since the first demonstration of a 694nm ruby laser nearly sixty years ago, lasers having been developed usinga variety of materials to provide a range of laser emission wavelengths.Consistent with the principles of photothermolysis, a laser wavelengthmay be selected to target specific tissues and body structures thatselectively absorb that wavelength, while leaving nearby tissues havingminimal absorption of the selective wavelength unaffected or minimallyaffected.

Examples include carbon dioxide lasers, developed in 1963 with awavelength of 10,600 nm, neodymium YAG lasers, developed in 1964 withwavelengths of 532 and 1064 nm, organic dye lasers, developed in 1966with a variety of wavelengths (for example, 585 and 595 nm), andalexandrite lasers, developed in 1979 and having a wavelength of 755 nm.Since the wavelength range of absorption varies with tissue type, havinga wide selection of laser wavelengths is critical to meeting the firstrequirement of selective photothermolysis (maximum absorption in thetarget tissue) for multiple tissues and thereby enabling a variety ofapplications. Following these inventions, multiple products subsequentlyemerged having many different laser sources and wavelengths tailored totarget a specific tissue and application. For example, pulsed dye laser(PDL) systems were developed for vascular applications since theiremission wavelength overlaps well with the absorption band ofhemoglobin. Carbon dioxide lasers were employed for skin resurfacingsince their 10,600 nm emission is strongly absorbed by water, theprimary chromophore in the dermis.

While individual laser systems tailored for specific applications (e.g.,treatment of specific tissues in specific medical applications) workswell, it requires a clinic or physician to purchase multiple systems tocover a full range of applications in a particular medical practice.This has led to the development of products with multiple lasers (e.g.,having different capabilities of wavelength/frequency, pulsewidth/duration, pulse energy and peak energy), which provides somebenefit but results in systems having higher cost, greater size/bulk,and complexity because of the higher number of system components.

More significantly, the number of laser wavelengths available frompractical, proven laser media, though significant at present, stillfails to cover the primary absorption bands for a number of importanttissue types. For example, commercially viable laser sources havingemission wavelengths in the near infrared (e.g., 780-2500 nm) and midinfrared (e.g., >2500 nm up to 10,000 nm) at clinically relevant outputlevels (e.g., pulse width & pulse energy) are especially limited. Forexample, the absorption bands of sebum (relevant for treating acne)includes absorption peaks at 1727 nm and 2305 nm. Similarly, theabsorption band for collagen includes peaks at 6049 nm and 6476 nm. Thelack of available laser sources at these emission wavelengths hasimposed significant limitations on the development of flexible systemscapable of treating these tissues. Similar limitations exist for othertissue types.

There is a need for systems having a wavelength tunable laser sourcethat is capable of providing laser emissions at wavelengths suitable fortreating a variety of tissue types. A variety of laser materials existthat are capable of producing laser emission over a broad, continuousspectral (wavelength/frequency) range, and are therefore tunable in thestrict sense. These include organic dyes, semiconductors, and someinorganic crystalline materials. However, significant technical barriersto such wavelength tunable laser sources have hindered developmentefforts.

One significant barrier to viable wavelength-tunable systems lies in thefact that the strength of the laser emission cross-section is inverselyproportional to the tunable range. Consequently, broadband tunable lasermaterials generally have low output powers that are unsuitable toapplications requiring high pulse energies. Applications in dermatology,for example, typically require treatment of relatively large body areas(e.g., 1 to 100 cm2), requiring high pulse energies on the order of 100mJ to 100 J per pulse to maintain therapeutic fluences over the area tobe treated. For this reason, broadband laser materials are not suitablefor many medical applications. In addition to the poor output power, thetunable range of such materials is typically too narrow to selectivelytarget more than one tissue type. Dermatological tissues may requireoutput wavelengths ranging from, e.g., visible wavelengths ofapproximately 500 nm to infrared wavelengths exceeding 10,000 nm.Currently available laser materials are inadequate to achieve such awide range of emission wavelengths with sufficient output powers totreat a full range of medical conditions, and there is a need forsystems capable of providing a variety of different wavelengths fortreating a variety of tissue types.

In addition to the capability of producing a wide range of laserwavelengths, dermatological laser systems capable of very short pulsedurations are also needed to treat a wide range of conditions. As noted,successful photothermolysis requires that the pulse duration pulse ofthe laser should be less than or equal to the thermal relation time(TRT). Heating in tissues depends upon both the absorption coefficientof the irradiated tissue structures for the wavelength of laser lightused, as well as their thermal relaxation times (TRT), which is ameasure of how rapidly the affected structure returns to its originaltemperature. Nanosecond lasers have been used for decades to treatpigmented lesions and tattoo removal. Nanosecond lasers, as used herein,are pulsed lasers having a pulse duration or pulse width (PW) of greaterthan 1 nanosecond (nsec) up to 1 microsecond (μsec). By delivering thelaser energy in a pulse with a very short time duration, highlylocalized heating (and destruction) of a tissue target structure (e.g.,melanin, ink particles, collagen) can be achieved, thereby minimizingdamage to non-target structures (e.g., non-targeted skin layers, bloodvessels, etc.). If the laser pulse duration is less than the TRT of thetarget tissue, no significant heat can escape into non-targetstructures, and damage to non-target structures is limited.

More recently, the availability of picosecond laser pulses has usheredin a new paradigm in tattoo removal because they offer the ability totarget tattoo ink particles at pulse widths that are equal or less thanthe TRT of the ink particles. As used herein, picosecond lasers arepulsed lasers having a pulse width or duration of 1 picosecond (psec) upto (and preferably below) 1 nsec. Studies have shown that the diameterof tattoo ink particles can range from 35 nm to 200 nm, with clusters aslarge as 10 μm. To clear the tattoo ink, the particles must be broken upinto smaller fragments that can be cleared by the body. To break theparticles up effectively, the laser energy must be delivered within theTRT of the particle, since the energy that escapes into the surroundingtissue not only damages non-target structures but also is unavailable tobreak down the target structure. A simple dimensional analysis showsthat the TRT of a spherical particle scales with the square of itsdiameter, and ink particles smaller than about 150 nm will haverelaxation times below 1 ns.

While the pulse duration for nanosecond lasers is generally less thanthe TRT for melanin in the skin, the small size of many ink particles intattoos can result in TRT times of less than 1 nanosecond for thoseparticles. Conventional Q-switched nanosecond lasers, which producepulses of 5-20 nsec in duration, may result in ineffective ink removalas well as damage to tissue structures as the pulsed laser energyescapes into adjacent non-target tissue structures after the lapse ofthe TRT of the ink particles. This is particularly true for lasershaving wavelengths that are highly absorbed by the non-targetstructures. Studies have shown that the use of picosecond lasers insteadof nanosecond lasers can reduce the number of treatment sessionsrequired to clear tattoos by a factor of 3.

Picosecond laser pulses may offer less tissue damage and higher safetymargins for pigmented lesions, in addition to their superior performancefor tattoo removal. The potential for improved clinical outcomes usingpicosecond lasers has resulted in commercially available systems havingpulse widths of 500-1000 psec with pulse energies (i.e., energy perpulse) exceeding 100 mJ. On the other hand, high-energy picosecondlasers are much more complex and costly than any other energy-basedtreatment systems in the dermatology market today, and there is a needfor more flexible, less expensive picosecond laser systems having a widerange of available wavelengths to treat a wide range of conditions.Additional details on treatment on treatment of tattoos is provided inrelated U.S. patent application Ser. No. 15/820,421.

The first commercial dermatological picosecond laser systems used eithera single 755 nm lasing wavelength, with alexandrite as the lasingmedium, or dual 1064 nm and 532 nm laser wavelengths using Nd:YAGlasers. The 755 nm and 1064 nm wavelengths are part of the near-infraredportion of the electromagnetic spectrum, and are well-suited to removalof black tattoo inks due to their broad absorption spectra. The 532 nmwavelength is in the green portion of the visible spectrum, and iswell-suited to removal of red inks which strongly absorb green light(the complementary color of red).

Because black and red are the most common tattoo colors, dual wavelength(532 nm and either 755 or 1064 nm) picosecond systems are the mostcommon systems available. However, green and blue inks occur in aboutone-third of tattoos, and the absorption strength for these inks isgreatest in the red portion of the visible spectrum. Accordingly, thereis a need for a red wavelength in addition to the dual wavelength1064/755, 532 nm (near infrared and green) picosecond laser systems tofacilitate removal of green and blue inks. In view of the already-highcost of picosecond laser systems, the addition of a red wavelength mustbe done at a low cost, and in a flexible system that allows differentwavelengths of light to be selected quickly and easily.

Because of their versatility, dual wavelength (1064/755, 532) picosecondsystems are widely used to treat benign pigmented lesions, which involvethe removal of melanin particles from the skin. Pulsed light at 532 nmis highly absorbed by melanin, while 1064 nm light absorbed less than10% as well (absorption coefficients of 55.5 mm⁻¹ and 4.9 mm⁻¹) poorlyabsorbed. In addition, penetration depth of laser light falls rapidlywith wavelength. Therefore, 532 nm laser light is effective ataggressive treatment of shallow pigment and 1064 nm light is morecommonly used for milder but deeper treatment. It would be useful tohave a third wavelength with an intermediate absorption in melanin,which could also help minimize potential damage to blood vessels in thesuperficial dermis, and maximize the absorption of melanin relative tohemoglobin.

Pulsed red light has been provided in prior art laser systems bylaser-induced florescence of organic dyes. However, dye-based lasersystems have a number of drawbacks. Typically, excitation is provided bya 532 nm (green light) Nd:YAG pulsed laser, with the red emissionwavelength determined by the specific dye being used. Wavelengths of585, 595, and 650 nm have been provided. The minimum pulse duration isdefined by the fluorescence lifetime of the dye, which is typicallybetween 1-5 ns, precluding their use in picosecond laser systems.Incoherent (non-laser) light may be captured optically and focused ontoa treatment plane.

In some systems, the dye cells may be used as the gain medium in a lasercavity to produce laser emission, in which case picosecond pulses arepossible because the pulse duration is approximately equal to that ofthe excitation laser. However, the cost of assembling such systems issignificantly increased relative to systems that do not require dyes,and becomes prohibitive if the dye cells must be replaced frequently.

A more fundamental limitation of dye systems is their susceptibility tooptical degradation. Both output energy and beam profile uniformity fallrapidly with operation, typically within 10,000 laser shots or pulses.Fluence of the beam at the treatment plane therefore becomes irregularand continues to change over time, leading to poor clinical outcomes.Emission also tends to have low spatial coherence, making it difficultto deliver the beam through a fiber or articulated are to an applicator,such as a handpiece, for application to the patient.

Because of optical degradation issues, dye cells are typically designedas a consumable item that attaches to the end of the applicator (e.g., ahandpiece). While this allows the user to change the dye cell whenperformance drops, restoring beam uniformity and fluence, it introducesseveral limitations. First, in multi-wavelength systems the dye cellmust be removed to change wavelengths, which is inconvenient to the userand patient during removal of multi-colored tattoos requiring multiplewavelengths in a single treatment session. Second, because the dye cellis near the point of application, integration of photometry to detectthe optical degradation is difficult because of space limitations. Inspite of these limitations, dye cells have seen limited but consistentuse in the field for decades because of their ability to providemultiple laser wavelengths.

Another known method for generating red-wavelength picosecond laserpulses is through second harmonic generation, in which the frequency ofthe pumping laser is doubled, resulting in an output having wavelengthsthat are half that of the pumping laser. For example, Nd:YAG lasingwavelengths such as 1319 or 1338 nm may be frequency doubled withnonlinear crystals to produce red picosecond pulses at 659 and 669 nm.However, pumping wavelengths capable of frequency doubling to providered laser light have relatively low optical gain, making the cost andcomplexity at these wavelengths significantly greater than existing 1064and 532 nm dual wavelength systems. In addition, wavelengths in the 1300nm range have limited use for dermatology, and such systems would haveonly one wavelength of significant value unless more than one laserengine is provided in the system, which would significantly increasesystem complexity, cost and bulk. Such systems are not economical andhave not been commercialized.

Finally, laser architectures outside of the red spectral region havebeen developed, but these systems sacrifice clinical efficacy because ofthe non-optimal wavelengths. For example, picosecond laser systems areavailable that produce 755 nm, near-infrared pulses using alexandrite asthe lasing medium, as well as systems that using 532 nm picosecondpulses to pump a titanium sapphire oscillator.

In addition to picosecond systems with visible light wavelengths totreat pigmented lesion, there is a need for systems capable of producingwavelengths in the near, medium, and far infrared systems for treatmentof other tissues. More specifically, there is a need for picosecondpulse laser systems capable of treating conditions in the near-infraredrange (approximately 780-2500 nm wavelengths) and in the mid-infraredrange (approximately 2500-10,000 nm wavelengths). These include, forexample, treatment of acne by targeting sebum, which has absorptionpeaks at 1726 and 2305 nm in the near-infrared range, and a number ofconditions involving collagen (e.g., wrinkles), which has absorptionpeaks at 6049 nm and 6476 nm in the mid-infrared range. The lack oftunable laser sources at these emission wavelengths with sufficientpulse power has imposed significant limitations on the development offlexible systems capable of treating such.

There is a need for dermatological picosecond laser systems that areable to efficiently treat a variety of medical conditions usingpicosecond pulse widths and a wide range of wavelengths from the visibleto the mid-infrared, and which are relatively compact, non-bulky andeasy to use. There is also a need for dermatological picosecond lasersystems having a simplified construction with fewer components, whichare capable of providing a variety of laser wavelengths for treatment ofa wide variety of pigmentation conditions and skin conditions, and allowa user to switch from a first to a second treatment wavelength quicklyand easily.

SUMMARY

In one embodiment, the invention comprises a dermatological treatmentsystem for treating a plurality of skin conditions using pulsed laserlight having a selected wavelength, comprising: a laser engine adaptedto output pulsed laser light having a first wavelength of from 500-1200nm, a pulse width of 10 psec to 10 nsec, and a first pulse energy offrom 100 mJ/pulse to 5 J/pulse; and at least one optical parametricoscillator (OPO) adapted to receive pulsed laser light from the laserengine and to generate OPO output pulses having a second wavelengthselected from a wavelength at which sebum tissue has a higher absorptioncoefficient than water and a wavelength at which collagen tissue has ahigher absorption coefficient than water, wherein the OPO output pulsescomprise one of OPO signal pulses and OPO idler pulses; and anapplicator adapted to receive and apply a selected one of the pulsedlaser light output from the laser engine and the OPO output pulses to atarget body tissue comprising sebum tissue, collagen tissue, and a thirdtissue that is neither sebum nor collagen.

In one embodiment, the invention comprises an optical parametricoscillator (OPO) system for use in a dermatological laser treatmentsystem, the OPO system comprising: an input coupler for receiving laserinput pulses having a pulse width of from 10 psec to 100 nsec and afirst wavelength, the input coupler comprising a mirror having a hightransmission (HT) at the first wavelength and a high reflectance (HR) atone of an OPO signal wavelength and an OPO idler wavelength; a resonantcavity including a nonlinear crystal having a crystal length between 5and 40 mm, wherein the resonant cavity produces OPO output pulses inresponse to receiving the laser input pulses, the OPO output pulseshaving a second wavelength selected from a wavelength at which sebumtissue has a higher absorption coefficient than water and a wavelengthat which collagen tissue has a higher absorption coefficient than water,wherein the OPO output pulses comprise one of OPO signal pulses and OPOidler pulses; and an output coupler comprising a mirror having a highreflectance (HR) at the first wavelength and transmitting a selectedportion of the second wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional illustration of skin tissue.

FIG. 2 is a graph illustrating the frequency of use of inks of variouscolors in tattoo designs.

FIG. 3 is a color wheel illustrating various colors and theircomplementary colors.

FIG. 4 is a graph illustrating the absorption spectra of red, green,blue, and black ink for various wavelengths of light.

FIG. 5A is a graph illustrating the absorption coefficients of melanin,venous blood, and arterial blood for various wavelengths of light.

FIG. 5B is a graph illustrating the melanin to blood absorption ratiofor venous and arterial blood for various wavelengths of light.

FIG. 6 is a block diagram of a system for treatment of dermatologicaltissue using pulsed laser light according to one embodiment of thepresent disclosure.

FIG. 7 is a block diagram of a prior art optical parametric oscillatorsuitable for use in dermatological treatment systems with nanosecondlasers.

FIG. 8 is a diagram of one embodiment of an OPO of the presentinvention.

FIG. 9 is a graph illustrating the absorption coefficients of sebum andwater for various wavelengths of light.

FIG. 10 is a graph illustrating the absorption coefficients of collagenand water at various wavelengths of light.

FIG. 11 is a block diagram of one embodiment of an OPO of the presentdisclosure.

FIG. 12 is a block diagram of an embodiment of a system for treatment ofdermatological tissue using pulsed laser light according to oneembodiment of the present disclosure.

DESCRIPTION

Exemplary embodiments of the present disclosure are illustrated in thedrawings, which are illustrative rather than restrictive. No limitationon the scope of the technology, or on the claims that follow, is to beimplied or inferred from the examples shown in the drawings anddiscussed here.

The present application discloses systems and methods for treatment of avariety of dermatological conditions using lasers, including systemsproviding a plurality of different wavelengths of laser light to provideimproved therapies for certain skin conditions, with at least one of thewavelengths being determined by an optical parametric oscillator. Insome embodiments, systems of the present disclosure permit rapidadjustment from a first treatment wavelength to a second treatmentwavelength, at a range of wavelengths including visible wavelengths,near-infrared wavelengths, and mid-infrared wavelengths.

Embodiments of the invention involve systems and methods for one or moreof treating a pigmentation condition in human skin (including withoutlimitation removal of tattoos and benign pigmented lesions) and skinresurfacing (including without limitation treatment of acne and otherscar tissue) using pulsed laser light having a high peak power (i.e.,power per pulse). Multiple wavelengths of laser light suitable for usein such systems and methods are provided using an optical parametricoscillator (OPO).

In one aspect, a system capable of providing picosecond laser pulses atthree or more different wavelengths suitable for treating pigmentationconditions and/or skin resurfacing is provided. In one aspect, a systemcapable of providing picosecond laser pulses at a plurality ofwavelengths for treating pigmentation conditions and/or skin resurfacingusing an OPO is provided. In one aspect, a system capable of providinghigh-energy, picosecond laser pulses at a plurality of wavelengths,including visible wavelengths and at least one of a near-infraredwavelength and a mid-infrared wavelength, is provided in a manner thatallows a user to select one of the plurality of wavelengths quickly andeasily.

In one aspect, a system capable of providing high-energy picosecondlaser pulses at plurality of visible wavelengths and at least one of anear-infrared wavelength and a mid-infrared wavelength is provided in amanner that may be added to an existing picosecond laser system. In oneaspect, a system for providing picosecond laser pulses at suchwavelengths that is capable of long-term operation without loss ofoutput energy or beam uniformity is provided. In one embodiment, thesystem is capable of provided more than 1 million laser pulses withoutsignificant loss of output energy or beam uniformity.

In one aspect, a tunable OPO capable of use in a dermatologicalpicosecond laser system is provided that allows a user to select adesired wavelength within a range of 1700-2360 nm is provided,preferably a desired wavelength within one of a first range of 1700-1770nm and a second range of 2280-2360 nm, more preferably a desiredwavelength of about 1726 nm or about 2300 nm. In one aspect, a tunableOPO capable of use in a dermatological picosecond laser system isprovided that allows a user to select a desired wavelength within athird range of 5900-9500 nm is provided, more preferably a desiredwavelength of about 6049 nm or about 6476 nm. In one aspect, a tunableOPO capable of use in a dermatological picosecond laser system isprovided that allows a user to select a desired wavelength within rangeof about 500-1200 nm, more preferably within one of a fourth range offrom 1400-1850 nm, a fifth range of from 1910-1950 nm, and a sixth rangeof from 2600-3500 nm.

In one aspect, methods for providing a dermatological treatmentaccording to one of the foregoing systems is provided.

FIG. 1 is a side view illustrating a cross-sectional view of a portion100 of the skin of a patient, including the outermost epidermis 110, themiddle layer or dermis 120, and the bottom layer or hypoderm is 130. Theepidermis 110 has a thickness of about 80-100 μm, which may vary frompatient to patient and depending on the area of the body. It includes upto five sub-layers and acts as an outer barrier. The outermost layer(the stratum corneum) consists of dead skin cells, which are constantlybeing replaced by new cells being made in the bottom layer (the stratumbasale).

The dermal layer has thickness of about 1-5 mm (1000-1500 μm). The inksin a tattoo design and the melanin in a pigmented lesion are bothlocated in the dermis. Consequently, laser light for removing tattoosand pigmented lesions must penetrate into the dermis. The dermiscontains the blood vessels, nerves, hair follicles, collagen and sweatglands within the skin. Careful selection of a number of parameters mustbe made avoid damaging many of these structures in the design andconstruction of laser systems for removal of tattoos and pigmentedlesions. For example, incorrect selection of the laser wavelength, pulsewidth, energy per pulse, the use (or nonuse) of a seed laser, or thepump energy of the laser source or amplifier may result in damage to oneor more of the foregoing structures in the dermis, as well as poorperformance in removal of the tattoo or pigmented lesion. Numerous othersystem choices, such as the use or non-use of an articulating arm fordelivery of the laser light to a handpiece for application to thepatient's skin, may also result in tissue damage and/or poor systemperformance if careful selection is not made.

The lowest layer of the skin is the hypodermis, which includes adiposetissue and collagen. The hypoderm is helps control body temperature byinsulating the structures of the body below the skin. In addition, thehypoderm is protects the inner body tissues from damage by absorbingshock and impacts from outside the body. Because the hypodermis containsfat, its thickness varies widely from person to person based on diet,genetic makeup, and other factors.

FIG. 2 is a graph illustrating the frequency of ink use of certaincolors in tattoo designs. Although black ink is the most frequently usedcolor in tattoo designs (79% of tattoos), red ink is the next mostfrequently used color, appearing in about 45% of tattoo designs. Darkblue ink is used in about one third (34%) of tattoos, followed closelyby yellow (32%) and green (30%) inks, respectively. Light blue ink isused in about one-fourth (25%) of tattoo designs.

FIG. 3 is a color wheel demonstrating the concept of complementarycolors, which are the colors opposite to a given color on the colorwheel. Thus, as previously noted, inks are more efficiently removed bylaser light of a complementary color. Because of the prevalence of greenand blue inks, it is desirable to have a system capable of reliablyproducing a red light wavelength in addition to the more widelyavailable 1064 nm and 532 nm wavelengths.

The light absorbance profile of a substance is determined by thechromophores (i.e., the light-absorbing portions of molecules) within itthat absorb light at particular wavelengths within the EMR spectrum. Thecolor of a substance (e.g., skin) is determined by the absorbanceprofiles of the chromophores within the visible light portion of the EMRspectrum. Sunlight, although seen as a homogenous white color, is acomposite of a range of different wavelengths of light in theultraviolet (UV), visible, and infrared (IR) portions of the EMRspectrum. A substance appears to the eye as the complementary color ofthe light wavelengths that are absorbed.

Laser-based removal of pigmentation occurs by applying light at highfluences (i.e., energy per unit area) such that thechromophore-containing compounds within the pigmented area (e.g., inkparticles in a tattoo or melanin in freckles or age spots) absorb somuch energy that the ink or melanin particles in the pigmented area areruptured or broken into small particles that may be removed by the body.

The more highly absorbed the wavelength of laser light by melanin (inthe case of pigmented lesions) and/or inks (in the case of tattoos), themore efficient the removal. Stated differently, less energy must bedelivered to rupture an ink or melanin particle if the wavelength of thelaser light being used is highly absorbed by the ink in the tattoo orthe melanin in the pigmented lesion. The absorption profile is only oneaspect of laser wavelength selection, however, and a wide range of laserwavelengths are used to remove tattoos and pigmented lesions, includingwavelengths in the visible and near-IR spectrum. Commercially availablesystems for removal of tattoos and pigmented lesions have used laserlight at 532 nm, 597 nm, 650 nm, 755 nm, 785 nm, and 1064 nm, amongothers.

FIG. 4 is a graph illustrating the absorption curves for various tattooink colors at a range of wavelengths. As previously noted, black ink(“ebony black”) has a high absorbance across a wide range of laserwavelengths. Accordingly, black ink in tattoos may be efficientlyremoved using a variety of different laser systems and wavelengths.

FIG. 4 also shows that red ink (“ruby red”) has a high absorbance at 532nm and nearby wavelengths, but its absorbance falls rapidly at higherwavelengths. Consistent with the concept of complementary colorsdiscussed earlier, the 532 nm wavelength corresponds with green light inthe visible spectrum, which is the complementary color of red.Accordingly, red light may be removed efficiently by 532 nm green laserlight but is poorly removed by, for example, 670 nm light in the redlight portion of the visible spectrum.

Conversely, FIG. 4 shows that green ink (“forest green”) has a highabsorbance of 660-670 nm red light. Thus, tattoos with green ink aremuch more effectively removed by 660-670 nm laser light that, forexample 532 nm green light, which is very poorly absorbed by green ink.Although green ink has a reasonable absorbance of near-infrared light at755 and 785 nm (absorbance of about 0.6 and 0.5, respectively), it hasmore than 50% greater absorbance at 660-670 nm wavelengths(absorbance >0.9) in the visible red portion of the spectrum.Accordingly, 660-670 nm red laser light may provide for removal of greeninks in tattoos with reduced laser intensity or fluence, fewertreatments sessions, or both, than green or near-infrared wavelengths.

FIG. 4 also illustrates that 660-670 nm red light will more efficientlyremove blue inks (“royal blue”) than near-infrared wavelengths such as755 and 785 nm. Although not as strongly absorbing of red light as greeninks, blue inks similarly show a much stronger absorption at a 670 nmwavelength than at 755 and 785 nm near-infrared (˜40% greater absorbancethan 755 nm wavelength and ˜50% greater absorbance than 785 nmwavelength). Accordingly, 660-670 nm red light offers improved removalof blue inks than current widely used wavelengths.

FIG. 5A is a graph illustrating the absorption curves for venal andarterial blood and melanin at various wavelengths of light. For removalof pigmented lesions, it is desirable to target melanin in the skin tothe exclusion of other structures, notably blood and blood vessels.Greater safety may be provided by wavelengths that are poorly absorbedby non-target structures. FIG. 5A illustrates that melanin is stronglyabsorbent at lower wavelengths of light in the red visible wavelengthsaround 650, but its absorbance decreases steadily to a very lowabsorption in the near-infrared region. The absorbance of venous andarterial blood, on the other hand, decrease rapidly from 600 nm throughabout 650 nm. Arterial blood (lower curve) decreases rapidly until arelatively flat absorbance profile in the range of 630-700 nm, with aminimum value around 680 nm. Venous blood decreases rapidly to about630-640 nm, then decreases more slowly to a minimum value at around 730nm.

Maximum safety margin is provided at wavelengths having the maximumdistance between the absorption curves of melanin on the one hand andvenous/arterial blood on the other. This occurs between about 670 nm andabout 700 nm, indicating that red laser light in this range willminimize damage to blood and blood vessels in the treatment of pigmentedlesions. Thus, it would be desirable to add a red laser light capabilityto existing 1064/532 nm dermatological systems.

FIG. 5B illustrates this in another way by graphically indicating theratio of the absorption ratios of venous and arterial blood to melanin.As the arterial blood curve demonstrates, melanin has its maximumabsorption relative to arterial blood at a wavelength slightly above 670nm. For venous blood, melanin reaches its relative peak at about 700 nm.Accordingly, red light in the 670-700 nm range, in addition to providingimproved removal of green and blue tattoo inks, also offers potentiallygreater safety in removal of pigmented lesions.

In one embodiment, systems of the present invention may provide pulsedlaser light at one or more wavelengths selected for efficient removal oftattoos having a wide range of ink densities. In one embodiment, a usermay select a wavelength within a desired range for at least a portion ofthe wavelength output range that the system is capable of producing. Inone embodiment, the laser pulses of the system have a pulse energyranging from 100-1500 mJ/pulse. In one embodiment, the laser pulses ofthe system have a peak power of 250 megawatt (MW) or higher, preferably500 MW or higher, more preferably 1 GW or higher. In one embodiment, adermatological treatment system provides laser light at a fluence of upto 5.0 J/cm². In one embodiment, a user may select a spot size (e.g., byadjusting the diameter of a laser beam) for treating a pigmentationcondition.

Some embodiments of the present invention involve high-energy pulsedlasers and an optical parameter oscillator (OPO) to provide a variety ofselectable wavelengths for one or more of treatment of pigmentationconditions and skin resurfacing. Applicants have discovered that OPOsmay be used to generate a range of pulsed laser wavelengths useful inremoval of tattoos and benign pigmented lesions. Producing of suchwavelengths using an OPO, however, requires a laser capable of producingrelatively high-energy pulses. As used herein, the term “laser engine”refers to a pulsed laser system capable of producing pulses having apeak power of 250 megawatt (MW) or higher, preferably 500 MW or higher,more preferably 1 GW or higher.

FIG. 6 is a schematic illustration, in block diagram form, of adermatological laser treatment system 600 using high-energy pulsed laserlight according to the present disclosure. A laser engine 620 isprovided to produce high-energy pulsed laser light at a desiredwavelength. Although a number of different laser engines are describedin the present disclosure, the description herein of certain laserengines should not be construed as excluding others not specificallydescribed. It will be appreciated by persons of skill in the art in viewof the present disclosure that a variety of different materials, designsand techniques may be employed to generate high-energy pulsed laserlight in systems of the present invention. Unless specifically excludedby the scope of the claims, all are considered to be within the scope ofthe present disclosure.

Laser engine 620 outputs laser pulses having a wavelength of from 1000nm to 1200 nm, a pulse width (PW) of 10 psec to 10 nsec, and a pulseenergy (PE) of 100 mJ/pulse to 5 J/pulse. In view of the fact that thepeak power is given by the pulse energy divided by the pulse power orPE/PW, it will be appreciated that a variety of pulse widths and pulseenergies may be used to produced high-energy laser pulses at a desiredwavelength and having a peak power of 250 megawatt (MW) or higher. Inone embodiment, laser engine 620 is a Q-switched laser.

A second harmonic generator (SHG) 630 receives the laser pulses from thelaser engine 620 and generates second harmonic laser pulses with awavelength that is half that of the pulses received from the laserengine 620. Many different crystals may be used for SHG, which resultsin an output signal having double the frequency and half the wavelengthof the pumping signal. In the case of 1064 nm (fundamental) and 532 nm(second harmonic) wavelengths, potassium titanyl phosphate (KTP) andlithium tetraborate (LBO) are common choices, although other crystalssuch as potassium dihydrogen phosphate (KDP) may also be used. Thecrystals typically have a length between 2 and 15 mm. Depending on whichmaterial is chosen, the laser engine pulses received by the SHG may notrequire focusing to achieve efficient conversion to the second harmonic.

An optical parametric oscillator (OPO) 640 receives the pulses from theSHG and provides two pulsed laser outputs, known as the “signal” and“idler” respectively. Both OPO outputs (i.e., the OPO signal pulses andthe OPO idler pulses) comprise laser light having a wavelength longerthan the light received from the SHG 630. Optical parameter oscillatorsoperate by receiving a pump laser signal (e.g., pulses as a firstwavelength), which is used to induce parametric amplification within anonlinear crystal in the OPO to produce the two output electromagneticfields (i.e., the OPO signal pulses and the OPO idler pulses). OPOs aretunable over a wide range of wavelengths and potentially offer theability to produce any desired wavelength within a range of desiredwavelengths.

An applicator 650 is provided to receive pulsed laser light 655 from oneor more of the laser engine 620, the SHG 630, and the OPO 640, and applythe received laser pulses to the skin of a patient for treating apigmentation condition or skin resurfacing. The applicator may comprisea handpiece adapted to be held in the hand of a user, such as aphysician or other healthcare provider, for treating the patient withpulsed laser light 655.

In some embodiments, the applicator may also comprise a selector (e.g.,a touchscreen on the applicator) allowing a user to select the pulsesfrom one or more of the laser engine 620, the SHG 630, the OPO (640)signal, and the OPO (640) idler for application to the skin of thepatient. A first output path 660 is provided to direct the output oflaser engine 620 to the applicator 650. In the embodiment of FIG. 6,first output path 660 comprises an optical multiplexer 665 between thelaser engine 620 and the SHG 630 to direct the laser pulses from laserengine 620 to the applicator 650. A second output path 670 is providedto direct the output of the SHG 630 to applicator 650. In the embodimentof FIG. 6, an optical multiplexer 675 located between the SHG 630 andthe OPO 640 directs the pulsed SHG output to the applicator 650. A thirdoutput path 680 is provided to direct the OPO signal output to theapplicator 650. In the embodiment of FIG. 6, an optical multiplexer 685located at the OPO signal output directs the OPO signal pulses to theapplicator 650. In some embodiments, as shown in FIG. 6, a fourth outputpath 690 is provided to direct the OPO idler output pulses to theapplicator 650. In the embodiment of FIG. 6, an optical multiplexer 695located at the OPO idler output directs the idler output pulses to theapplicator 650. In some embodiments, optical multiplexer 695 is omitted.In some embodiments (not shown) a single optical multiplexer and outputpath may be provided for both the OPO signal pulses and the OPO idlerpulses.

In some embodiments, one or more of optical multiplexers 665, 675, 685,and 695 may be selectable by a user, e.g., by a rotatable mirror (notshown) from an interface located on the applicator 650, to allow theuser to choose one among a plurality of available wavelengths of lightto be routed to the applicator 650 to treat a patient. In addition,although the embodiment of FIG. 6 illustrates each of the first, second,third and fourth output paths, in alterative embodiments (not shown),one, two, or three of the four output paths shown may be omitted, suchthat pulses for one or more of the laser engine 620, the SHG 639, andthe OPO 649 may not be available to treat a user. Although not shown inFIG. 6, one or more beam dumps may also be selectable by a user to shuntthe laser pulses from one or more of the laser engine 620, the SHG 630,the OPO 640 signal output pulses, or the OPO 640 idler output pulses.

Although laser systems according to FIG. 6 may be constructed in anumber of different physical layouts, a housing or chassis (not shown)may be used to provide store and protect some or all of the foregoingoptical components. In one embodiment (not shown) a movable console(e.g., a wheeled cart) may function as a housing to house the laserengine 620, the SHG 630, the OPO 640, and the optical multiplexers 665,675, 685, and 695. In one embodiment, an articulated arm having anoptical medium (e.g., one or more waveguides) therein may be used toprovide an optical path for the optical multiplexers 665, 675, 685, and695 to direct pulses for a selected one of the laser engine 620, the SHG630, the OPO 640 signal output, and the OPO 640 idler output pulses tothe applicator (e.g., to a handpiece constructed and arranged to be heldin the hand of a user). In one embodiment, a movable console may beprovided as a housing to house the laser engine 620, SHG, and opticalmultiplexers 665 and 675, with the OPO 640 and optical multiplexers 685and/or 695 located in an applicator such as a handpiece.

Finally, a controller 605 is provided, together with appropriateelectrical circuitry, to control the operation of the dermatologicallaser treatment system of FIG. 6. In one embodiment, the controller 605controls the operations, including the electrical operations, of one ormore (and preferably all or most) of the laser engine 620, the SHG 630,the OPO 64, and applicator 650. In one embodiment, the controller 605controls the operations of one or more of the laser engine 620, the SHG630, the OPO 640, and multiplexers 665, 675, 685 and 695.

Laser engine 620 may comprise any of a number of designs to achievestable, high-energy pulses, and all such designs are intended to bewithin the scope of the invention. In one embodiment (not shown), laserengine 620 comprises a seed laser providing a pulsed initial lasersignal for further amplification by an amplifier. Seed lasers arefrequently used to produce a low power initial signal that may beamplified to obtain a final laser signal having desired characteristic.Many characteristics that may be desired in the final signal (e.g.,short pulse widths, a wavelength having a narrow spectral line width)are easier to produce in a seed laser than in a single, high-powerlaser. The seed laser signal may then be easily amplified to obtain alaser signal having desired characteristics.

Although many seed lasers produce pulses having a pulse energy of 1 μJor less, in one embodiment, a high-power seed laser is provided. Thehigh-power seed laser is capable of producing pulses of at least 100 μJper pulse, more preferably 100 μJ to 10 mJ, with a narrow linewidth anda wavelength of from 900-1200 nm, as well as a pulse width of 1 psec to100 nsec. In one embodiment, the seed laser produces pulses having astable polarity, and may be constructed and arranged to produce otherdesirable characteristics to enable the amplifier to output high-energyoutput pulses having a pulse energy of 100 mJ to 5 J, more preferably500 mJ to 5 J, a wavelength of 1000-1200 nm, and a pulse width of 200psec to 10 nsec. The pulses in seed laser have a relatively high peakpower that may be amplified to obtain high-energy pulses as required bylaser engine 620. In various embodiments, the seed laser may take theform of many oscillators known in the art to produce picosecond pulsesincluding fiber lasers, microlasers, or diode lasers.

The pulsed output of the seed laser is received by an amplifier (notshown), which amplifies the output of the seed laser to produceamplified laser light having the same pulse width and wavelength as theseed laser, but with a greater pulse energy. In one embodiment, theamplifier amplifies the seed laser pulses by a factor of 1000 or more.The amplified laser pulses output from the amplifier may, in someembodiments, be output (e.g., to an applicator such as applicator 650)and used to treat a dermatological condition of a patient. Multipleapproaches in the art are known for amplifiers that will amplify lasersignals to a pulse energy of >100 mJ, including >500 mJ.

In one embodiment (not shown), laser engine 620 may comprise a highpower oscillator. In one embodiment (not shown), laser engine 620 maycomprise a hybrid modelocked laser combining the functions of a laseroscillator and amplifier into a single cavity. Other approaches may alsobe used to produce appropriate laser engines 620.

There are a number of challenges to producing an OPO capable of pulseenergies of 50 mJ/pulse or greater for picosecond lasers. For optimizeddesigns, the conversion efficiency of pump light to output (signal andidler) is about 30-50%. Because of the high energies involved,relatively large beam diameters must be used to avoid exceeding thethreshold intensity to damage to optical structures within the OPO. Inaddition, the cavity length must be limited to enable the light to makeat least 10-30 round trips across the cavity during the pulse duration(or width) to enable the signal and idler fields to build up to maximumenergy. This results in a scaling law of about 1 cm/ns for the maximumcavity length vs. pump pulse duration. Thus, for a nanosecond laserhaving a pulse duration of 5 ns, the cavity length should be limited to5 cm or less. For a picosecond pulse, the cavity length should thus belimited to less than 1 cm. However, it is not possible to simply makethe cavity very small because cavity length is inversely related to beamquality, as explained below.

The combined constraints of large beam diameter and short cavity lengthimposed for achieving high pulse energies (50 mJ/pulse or greater) forpicosecond pulses creates a fundamental challenge for OPO performance,because they result in the cavity having a high Fresnel number,expressed as N=d²/(4Lλ), where N, d, L, and λ are Fresnel number, beamdiameter, cavity length and wavelength, respectively. Thus, because theFresnel number varies inversely with the cavity length L, the smallerthe cavity length, the larger the Fresnel number. It is well-known thatoptical cavities with N>>1 are prone to lasing many transverse opticalmodes, and therefore have low beam quality.

Beam quality in laser systems is typically expressed as M², whichprovides a measure of the spatial coherence of the beam and thereforehow well it can maintain collimation over a given distance. The largerthe value of M², the higher the divergence angle of the beam (i.e.,lower values indicate higher beam quality). The M² parameter is acritical measure for laser emission because it impacts the complexity ofthe optical delivery system design. For high energy picosecond medicallaser systems requiring an articulated arm to deliver the beam to theapplicator (e.g. a handpiece), the larger the value of M², the largerthe diameter of the arm required to accommodate the divergenceassociated with the deterioration of the beam quality.

An example of a proposed OPO design illustrates the problem. In an OPOdesign proposed by Rustad et al. (FIG. 7) loss of beam quality wasaddressed by using two nonlinear crystals C1 (730) and C2 (740) withorthogonally oriented beam walk-off axes and tuning of the signalwavelength to 670 nm to induce absorption of the idler pulses 770 in oneof the crystals. The Rustad design proposes a 5 nsec pulse 710 having aninput pulse energy of 120 mJ, a beam diameter of 6 mm, and a pulsewavelength of 532 nm. An input coupler mirror 720 is highly reflective(HR) at the 670 nm OPO signal wavelength and highly transmissive (HT) atthe 532 nm pump or input wavelength. An output coupler 750 has highreflectance (HR) at the 532 nm pump wavelength and 35% reflectance atthe 670 nm OPO signal wavelength, outputting OPO signal pulses 760having a pulse energy of approximately 50 mJ. OPO 700 also producesidler pulses 770, shown in FIG. 7 for illustration as being output fromoutput coupler 750 but which were, according to Rustad et al., absorbedwithin nonlinear crystals 730 and/or 740.

In simulations, Rustad et al. demonstrated that walk-off in orthogonalaxes and absorption of the idler signal within the crystals 730, 740 maybe combined to achieve a beam quality parameter M²≈2. Without idlerabsorption, the beam quality decreased to M²≈8. They also determinedthat the maximum efficiency is achieved when both crystals were 20 mmlong. The cavity had a Fresnel number of N=335, indicating that theRustad design significantly improved expected beam quality.

However, the Rustad et al. design is not well suited to use inpicosecond laser systems. Applying the foregoing scaling law for a 750psec pulse, the cavity is limited to less than 1 cm (about 0.75 cm inlength), which is insufficient length to provide two nonlinear crystalsof adequate length. More significantly, a 750 psec pulse increases thepeak power of the pulse by a factor of 6 compared to a 5 nsec (5,000psec) pulse. Thus, to keep the fluence the same and avoid damaging theoptical components of the OPO, the beam area must also be increased by afactor of 6.6 and the beam diameter by a factor of 2.6. This wouldresult in a cavity Fresnel number of N=9080 and a beam quality ofM²>500.

The present applicants have developed an OPO usable in picosecond lasersystems that is adapted to overcome the limitations of conventionaldesigns while maintaining high beam quality.

In one aspect, the present disclosure provides a tunable OPO capable ofproviding tunable emission wavelengths from visible to infrared for usein a dermatological laser treatment system. The first opticalparametrical oscillator was developed in 1965 at Bell Labs. OPOs use anonlinear optical crystal pumped by a laser pulse to producesimultaneous emission at a signal wavelength and an idler wavelength.The signal and idler wavelengths may be tuned throughout a range ofwavelengths by adjusting either the crystal temperature or its angle ofincidence with respect to the laser pump beam. OPOs may be designed withthe signal and idler wavelengths in the visible and infrared spectralrange.

Although high-energy pulsed OPOs have been long recognized as capable ofproducing optical emission over a broad spectral range, their commercialapplication to date has been limited, primarily because the conversionof pump emission to the signal and idler wavelengths proceeds by anon-linear process and is inefficient unless the pump pulse has a veryhigh peak power, on the scale of 1 GW. Because of the cost and size,GW-level pulsed laser sources have not been commercially viable. Inaddition, the overall system complexity typically requires opticalelements to be periodically realigned. Because of these factors, OPOshave until very recently been limited been limited to scientificinstruments that require periodic tuning by the user. There is a need inthe medical field for improved pulsed laser systems using OPOs toproduce tunable emission at multiple spectral ranges, and a compact,simplified laser pump engine producing laser pulses with pulse energieson the order of 1 J and peak powers of approximately 1 GW.

Scientific lasers producing such output levels typically use a masteroscillator power amplifier (MOPA) configuration in which a simple andcompact oscillator produces a low-energy seed laser pulse that is thenamplified to a final pulse energy in an amplifier. Common compact seedoscillators include diode and fiber lasers with pulse energies in the 1nanojoule (nJ) to 100 microjoule (μJ) range. Since the gain of mostoptical amplifiers is limited to 10 to 100 because of parasitic effectssuch as amplified spontaneous emission (ASE), a complex series ofamplifiers are needed to amplify the seed pulse to 1 J.

In one embodiment, the OPO is pumped by a pulsed laser engine using amicrolaser oscillator to produce the seed pulse. Microlasers are verycompact (approximately 1 cm long), passively Q-switched lasers that havebeen demonstrated to produce pulse energies up to 1 mJ with pulsedurations of 200-1000 psec. The main elements of a microlaser include ahigh reflectance (HR) mirror, a laser gain crystal, a saturable absorber(passive Q-switch), and an output coupler. Since the peak power can beon the order of 2 MW (=1 mJ/500 psec), which is 10 to 100,000 timeshigher than common seed lasers, the number of amplifiers and thus thecomplexity of the amplifier design can be reduced dramatically.

However, high-energy (>100 μJ) microlasers have notoriously poor pulseenergies and spatial beam quality. To achieve high pulse energy, a largemode size (approximately 500 μm diameter) must be used. Because of theshort (approximately 1 cm) cavity length, this results in a cavity witha high Fresnel number that is very sensitive to optical misalignment. Toovercome this, some embodiments use a monolithic microlaser in which thecomponents are permanently bonded together such that misalignment is notpossible.

Another complication of microlasers is their tendency to produce laseremission with unstable polarization properties. Any polarizationinstability in the microlaser output will be carried through to thefinal output of the amplifier. Conversion of pump energy to signal andidler wavelengths in an OPO is sensitive to the pump polarization, so itis important in embodiments of the present invention for the microlaserto have stable output polarization to be used as the seed laser for thelaser engine to pump the OPO. Because of the short microlaser cavitylength, integration of common polarization controlling intra-cavityoptical elements such as polarizers and Brewster plates is notpractical. Thus, in some embodiments, the present invention incorporatesa grating waveguide mirror (GWM) for the microlaser output coupler tocontrol its output polarization.

In some embodiments, both the fundamental wavelength of the amplifieremission as well as its second harmonic can be used to pump the OPO. Ingeneral, the tuning ranges of the OPO signal and idler wavelengthsdepend on the pump wavelength. Having multiple pump wavelengthsavailable from the same pump engine can expand the total availablespectral coverage from one or more OPOs. For example, if Nd:YAG is usedas the laser material for the laser pump, the 1064 nm emission could beused to pump an OPO directly, or it could also be used to produce 532 nmlight that is subsequently used to pump an OPO. Thus, in someembodiments, the second harmonic of the laser engine wavelength isobtained by second harmonic generation (SHG) in a nonlinear crystal.

In some embodiments, OPO-based systems of the present disclosure arecapable of producing a wide range of temporal pulse formats. Aspreviously noted, one of the requirements for achieving selectivephotothermolysis of a target tissue is that the laser pulse durationmust be smaller than the thermal relaxation time of the target tissue.In fact, the pulse duration is typically set to 50 to 100% of thethermal relaxation time since further shortening doesn't significantlyimprove thermal confinement of the absorbed laser energy in the targetbut can limit the maximum fluence that can be used.

In some embodiments, the laser engine of the dermatological treatmentsystem may be adapted to operate in one of a first treatment mode or asecond treatment mode. In the first treatment mode, which may bereferred to as “pulse mode,” the laser engine outputs individual pulsesat a pulse frequency of from 0.1 Hz to 100 Hz. Such pulse formats may beused on tissues with short thermal relaxation times (TRTs). In thesecond treatment mode, which may be referred to as “burst mode,” thelaser engine outputs a plurality bursts at a burst frequency of 1 Hz to100 Hz. Each burst comprises a plurality of individual pulses, with thepulses within the burst having a pulse frequency greater than 100 Hz,and preferably greater than 1000 Hz. Each burst is characterized by aburst duration of from 500 μsec to 50 msec, a burst energy of from 10 mJto 20. In some embodiments, a user interface may be provided by whichthe user may select the laser engine to operate in pulse mode or inburst mode. The user may also specify one or more of the foregoingparameters defining the pulse mode (e.g., pulse frequency) or burst mode(e.g., burst frequency, pulse frequency within the burst, burstduration, burst energy, etc.), and may also select one or more laserengine parameters.

For example, when treating tattoos, the user may select pulse modeoperation, and may specify a 750 psec pulse duration with a pulsefrequency between 1 and 10 Hz. In this case, the microlaser is simplydriven at the desired pulse frequency with each 750 psec pulse amplifiedand acting as an individual treatment pulse. However, when treatingblood vessels, which have a longer TRT than tattoo ink particles, it maybe desirable to have a longer pulse duration, which may be from about1-10 msec. In this case, the user may select burst mode operation toproduce a 1-10 msec long burst of pulses at high repetition rate (e.g.,individual pulse rate of 10,000 Hz). If the pulse duration is muchshorter than 10 msec, the burst will appear to the tissue like acontinuous 10 msec pulse. Because microlasers have such a short cavitylength, the pulse build-up time is short and therefore they are wellsuited for operation at high repetition rates.

In one aspect, the present disclosure provides dermatological treatmentsystems incorporating multiple OPOs that are each tuned (or are tunableby a user) to different wavelengths within a selected range ofwavelengths to provide a wide range of spectral coverage. In someembodiments, the laser engine is located within a housing, which mayalso enclose various optical multiplexers and power sources, etc. Thelaser pulses may be applied to the tissue of a patient using anapplicator that may comprise a handpiece adapted to be held in the handof a user such as a physician or technician.

In some embodiments, the OPOs may be located in the housing while inother embodiments the OPOs may be located within the applicator. Instill other embodiments, some OPOs may be located in the housing andsome OPOs may be located within the applicator. In some embodiments, aplurality of applicators, each having an OPO that is tunable within aspecific range of wavelengths, may be attachable to and detachable fromthe laser engine and/or an SHG output to provide pulse mode or burstmode delivery of therapy to a target tissue. In one embodiment, anarticulating arm may be used to couple the one or more handpieces to thelaser engine and/or SHG. One advantage of such an approach is that auser may purchase OPO-containing handpieces as an accessory and thesystem may be a modular, expandable system.

FIG. 8 is a schematic view of the optical elements of an opticalparametric oscillator 800 according to one embodiment of the presentinvention. The OPO is adapted to be used in dermatological lasertreatment systems having pulse energies of 50 mJ/pulse or higher. A pumplaser providing pulses 810 is used to induce parametric amplificationwithin a nonlinear crystal 830 to produce OPO signal pulses 840 and OPOidler pulses 850. The wavelengths of both the OPO signal pulses 840 andthe OPO idler pulses 850 may be adjusted (or tuned) to achieve a desiredwavelength with a wide range of possible wavelengths. Adjustments may bemade, in different embodiments, by alteration of the crystal orientation(e.g., angle relative to the optical axis) or temperature.

For dermatological applications the ability to selectively damage targettissues or tissue structures is strongly determined by laser wavelength.Accordingly, embodiments according to the present disclosure offer thepotential to select a desired wavelength within a wide range ofavailable wavelengths to obtain the optimum wavelength for a particulartarget tissue or structure, in stark contrast to current dermatologicalapproaches where the available wavelengths are limited to the atomicemission lines of the laser material being used and its harmonicwavelengths.

As already noted in connection with FIG. 6, in various embodiments ofthe invention the OPO 800 may be located in a console or housing, or inan applicator such as a handpiece. In some embodiments, the OPO 800 islocated in the console or housing to enable wavelengths to be rapidlychanged by a user and to enable the use of an articulated arm to deliverany of the available wavelengths to a single handpiece. The dimensionsof typical articulated arms are about 15-20 mm ID and 1.5 meter length,and require a beam to have a beam quality of M²˜100 to avoid clippingthe beam (because of beam divergence) inside the articulated arm.Accordingly, it is necessary to improve beam quality from M²>500 toM²˜100, without relying on multiple crystals or extending the cavitylength beyond 10 mm.

The present invention provides those results in a single-crystal designthat, contrary to prior designs, enables absorption of the OPO idlerpulse wavelength within the OPO crystal to improve beam qualitysufficiently to enable delivery through an articulated arm.

Referring again to FIG. 8, in one embodiment, nonlinear crystal 830comprises a BBO (beta barium borate) crystal positioned between a pairof flat mirrors 820, 840 defining the OPO optical cavity. In oneembodiment, a first mirror 820 serves as an input coupler and has hightransmission (HT) at 532 nm and is highly reflective (HR) at the OPOsignal wavelength, which in various embodiments may range from 575-750nm, 620-720 nm, 660-680 nm, and about 670 nm. A second mirror 840 servesas an output coupler and transmits a portion of the signal wavelength.Second mirror 840 may be constructed to achieve a desired signaltransmission from, e.g., 10-99%, preferably 25-75%, more preferably40-60%, more preferably about 50%. The pump pulse width (or duration)may range from 1 psec to 1 nsec, preferably 100 psec to <1 nsec, morepreferably 500-750 psec. In various embodiments, nonlinear crystal 830may have a length of 5-25 mm, preferably 5-15 mm, and more preferablyabout 10 mm. In one embodiment, the pump beam has a diameter between 4and 15 mm, more preferably about 10 mm.

The OPO 800 may have an efficiency of about 25% or higher, preferably35% or higher. In one embodiment, OPO 800 is capable of receiving pumplaser input pulses 810 at a wavelength of from 525-535 nm and having apulse energy of 100 mJ/pulse to 5 J/pulse, and outputting OPO signalpulses 850 having a wavelength of from 620 nm to 720 nm and a pulseenergy of about 50 mJ/pulse to about 2.5 J/pulse. In one embodiment, OPO800 is capable of receiving pump laser input pulses 810 at a wavelengthof from 525-535 nm and having a pulse energy of 100 mJ/pulse to 1J/pulse, and outputting OPO signal pulses 850 having a pulse energy ofabout 25 mJ/pulse to about 500 mJ/pulse. In some embodiments, the OPO iscapable of outputting both OPO signal pulses 850 and OPO idler pulses860. In some embodiments, all or a portion of the OPO idler pulses areabsorbed in the nonlinear crystal 830. In one embodiment, the nonlinearcrystal may absorb from 10-75% of the OPO idler pulse energy, morepreferably from 20-60% of the OPO idler pulse energy.

The signal and idler wavelengths λ_(s) and λ_(i) are related to the pumpwavelength λ_(p) by energy conservation through the equation

$\frac{1}{\lambda_{p}} = {\frac{1}{\lambda_{s}} + \frac{1}{\lambda_{i}}}$

For a given pump wavelength, increasing the signal wavelength willdecrease the idler wavelength and vice versa. In cases whereoptimization of the signal is desired, idler absorption may be used toreduce the M² of the signal (i.e., to improve signal quality) and theOPO may be adjusted to a signal wavelength where the idler experiencessufficient absorption to reduce the M² to support practical beamdelivery to the patient surface. When the OPO is located within thehousing of the system, an M² of ˜100 is desirable to allow for areasonably narrow arm diameter that such that the arm is ergonomic andnot too costly. Even when the OPO is located in the applicator, it maybe desirable to use idler absorption to help limit the M² in order tosupport a practical working distance and avoid the need for highnumerical aperture optics within the applicator.

In one embodiment, BBO is used for the OPO crystal material since thetransmission of BBO drops gradually from 100% at 2000 nm to <5% at 3500nm. Using the equation above, we see that signal wavelengths from 630 to730 nm will produce idler wavelengths of between 3420 and 1961 nm for a532 nm pump. Higher idler absorption improves the M² but will alsoreduce the signal output energy. Therefore, a range of red wavelengthsare possible and can be selected depending on the relative importance ofsignal pulse energy and M² for a given application. In on embodiment,transmission through an articulated arm facilitated by selection of 670nm as the OPO signal wavelength, in which case the M² will be ˜100 andsingle-pass idler absorption is ˜30%.

In one aspect, the present disclosure provides an OPO for use in adermatological laser treatment system for treating at least one of sebumtissue (e.g. the sebaceous glands) and collagen tissue of a patient. Thesystem includes at least one OPO capable of producing OPO output pulseshaving a wavelength selected to damage sebum tissue for treating activeacne or collagen (e.g., for treating wrinkles). In some embodiments,separate OPOs are provided for targeting sebum tissue and collagen,e.g., a first OPO having an emission wavelength targeting sebum, and asecond OPO with an emission wavelength targeting collagen.

FIG. 9 is a graph illustrating the absorption coefficients for sebum andwater at various wavelengths. For clarity, the curve showing a peak atapproximately 1900 nm is the absorption coefficient for water, while thecurve showing a double peak between 2200 and 2400 nm is the absorptioncoefficient for sebum. Both of the absorption coefficient curves areread on the left-side vertical scale. The curve showing a large peakbetween 1600 and 1700 nm is the penetration depth of light in water,which is read on the right-side vertical scale. As shown in FIG. 9,there are wavelength ranges, with peaks near 1726 nm and about 2305 nm,in the absorption spectrum of sebum at which the absorption coefficientexceeds that of water. More specifically, the absorption coefficient ofsebum tissue exceeds that of water at wavelengths of about 1700-1770 nm,and at wavelengths of about 2280-2360 nm. Wavelengths within thesewavelength ranges offer the possibility to selectively damage thesebum-filled glands without harming surrounding non-sebum tissues, forwhich the predominant chromophore is water. It is believed that laserpulses of about 10 J and having a pulse duration less than 200 msec arecapable of targeting sebum at a wavelength of about 1726 nm.

FIG. 10 is a graph illustrating the absorption coefficients for collagenand water at various wavelengths. FIG. 10 demonstrates that there arewavelength ranges, with peaks near 6049 nm and about 6476 nm, in theabsorption spectrum of collagen at which the absorption coefficientexceeds that of water. More specifically, the absorption coefficient ofcollagen tissue exceeds that of water at wavelengths of about 5900-9500nm. Wavelengths within these wavelength ranges offer the possibility toselectively damage the collagen without harming surrounding non-collagentissues, for which the predominant chromophore is water. It is believedthat skin resurfacing using embodiments of the present invention totarget collagen may involve pulse durations of 0.5-10 msec toselectively target collagen at the foregoing wavelengths.

FIG. 12 discloses simplified block diagram illustration of adermatological laser treatment system 1200 that may be used to providetreatments for medical conditions involving targeting of sebum and/orcollagen. In one embodiment, producing picosecond pulses and having oneor more OPOs tuned to a wavelength in the ranges noted in connectionwith FIGS. 9 and 10 may be used to treat sebum or collagen. The system1200 includes a laser engine 1220 to generate and output high-energypulsed laser light a one of a plurality of desired wavelengths on anoutput path 1270. Although different laser engines are disclosed anddescribed herein, such descriptions should not be construed as limitingor excluding others. Persons of skill in the art, having the benefit ofthe present disclosure, will appreciate that a variety of differentmaterials, designs and techniques may be used to generate high-energylaser pulses, and unless specifically excluded by the scope of theclaims, all are considered to be within the scope of this disclosure.

In one embodiment, laser engine 1220 may comprise a diode laser 1202, amicrolaser 1204, and a laser amplifier 1214 to produce pulses having afirst wavelength of from 500-1200 nm, a pulse width (PW) of 10 psec to10 nsec, and a first pulse energy (PE) of 100 mJ/pulse to 5 J/pulse. Itwill be appreciated that a variety of pulse widths and pulse energiesmay be used to produced high-energy laser pulses at the foregoingwavelengths and having a peak power in the range of 250 MW or higher.

In one embodiment, the laser engine 1220 may operate in a firsttreatment mode that is a pulse mode of operation, and may produceindividual treatment pulses at a pulse frequency of 0.1 Hz to 100 Hz. Inone embodiment, the laser engine 1220 may operate in a second treatmentmode that is a burst mode of operation to produce bursts of laser pulsesat a burst frequency of 1-100 Hz. Each burst comprises a plurality ofindividual pulses having a pulse frequency greater than 100 Hz, and insome embodiments greater than 1000 Hz. The bursts have a burst durationof 500 μsec to 50 msec, and a burst energy of from 10 mJ to 20 J.

A laser engine controller (not shown) may be provided in someembodiments to allow a user to select one of the pulse mode of operationor the burst mode of operation. The laser engine controller may includeone or more of hardware (e.g., a microprocessor), software, or firmwareto control the function and operation of one or more components of thelaser engine. In some embodiments a user interface (not shown) may becoupled to the laser engine controller, and the user may select one ofthe first or second treatment mode, and may control one or more of theforegoing parameters of the laser engine pulses or pulse bursts, via theuser interface.

Referring again to FIG. 12, the dermatological laser treatment system1200 includes an OPO 1240 that is adapted to receive pulsed laser lightfrom the laser engine 1220 along output paths 1270, 1260, 1300. As notedabove, OPOs produce simultaneous emission of pulses at an OPO signalwavelength and an OPO idler wavelength when pumped by laser light fromthe laser engine 1220. The OPO may be constructed and arranged togenerate OPO output pulses having a second wavelength selected from a) awavelength at which sebum tissue has a higher absorption coefficientthan water and b) a wavelength at which collagen tissue has a higherabsorption coefficient than water. Depending upon its construction andtuning, the OPO 1240 may use either of the OPO signal pulses and the OPOidler pulses as OPO output pulses. The OPO 1240 outputs the outputpulses (whether signal or idler wavelength pulses) along an output path1280.

The dermatological laser treatment system 1200 also includes anapplicator 1250 adapted to receive and apply (e.g., using one or moreoptical multiplexers 1265, 1275, 1285), one of the pulsed laser lightoutput from the laser engine 1220 and the OPO 1240 for application to atarget tissue of a patient. As shown in FIG. 12, applicator 1250 mayreceive pulsed laser light from the laser engine 1220 along optical path1270, 1260, 1275, 1330, 1290, and may receive pulsed light from OPO 1240along optical path 1280, 1290. In one embodiment, the applicator mayapply the pulsed laser light from the laser engine 120 to a third targetbody tissue that is neither sebum tissue nor collage tissue. Based onthe wavelength output from the OPO 1240, the applicator may receive theOPO output pulses and apply them to a target body tissue comprisingsebum tissue or collagen tissue.

In some embodiments (not shown) multiple OPOs 1240 may be provided toenable the dermatological laser treatment system 1200 to generate avariety of treatment wavelengths for targeting a variety of tissuetypes. Although OPOs may in some embodiments be tunable by adjustingtheir position or temperature, a given OPO may be tunable only in aparticular wavelength range. For example, an OPO 1240 designed to targetsebum tissue may not be adjustable to generate wavelengths havingsufficient power to target collagen tissue, and vice versa. Accordingly,in one embodiment (not shown) a first OPO 1240 is provided to receivepulsed laser light from the laser engine 1220 at a first wavelength andto generate OPO output pulses having a second wavelength at which sebumtissue has a higher absorption coefficient than water, and a second OPO(not shown) is also provided to receive pulsed laser light from thelaser engine 1220 at the first wavelength and to generate OPO outputpulses having a third wavelength at which collagen tissue has a higherabsorption coefficient than water. Additional optical multiplexers (notshown), similar to optical multiplexers 1265, 1275, 1285, may beprovided to enable a user to select an optical path to input light fromone of the laser engine 1220 and the SHG 1230 into one of the first OPO1240 and the second OPO. For example, laser light from the SHG 1230 maybe input to the first OPO 124 along optical path 1270, 1310, 1320, 1300.A similar optical path (not shown) may be provided using opticalmultiplexers to allow light from the laser engine 1220 or the SHG 1230to be input to the second OPO (not shown). In a still further embodiment(not shown), additional optical multiplexers may be provided to enablean output from one of the first OPO 1240 and the second OPO to be usedas an input into the other of the first OPO 1240 and the second OPO toprovide additional user-selectable output wavelengths from the system1200.

In a still further embodiment, a third OPO (not shown) is provided totarget tissue that is neither sebum nor collagen. The third OPO mayreceive pulsed laser light from the laser engine 1220 at the firstwavelength and to generate OPO output pulses having a fourth wavelengththat is a wavelength at which water has a higher absorption coefficientthan sebum tissue and collagen tissue. In another embodiment (not shown)the third OPO may receive laser light from the SHG 1230. In specificembodiments, the second wavelength is a wavelength within one of a firstrange of from 1700-1770 nm and a second range of from 2280-2360 nm, thethird wavelength is a wavelength within a third range of 5900-9500 nm;and the fourth wavelength is a wavelength within one of a fourth rangeof from 1400-1850 nm, a fifth range of from 1910-1950 nm, and a sixthrange of from 2600-3500 nm

In multi-OPO embodiments, the dermatological laser treatment system 1200may comprise an OPO selector (not shown), allowing a system user toselect one of the first OPO 1240, the second OPO (not shown), the thirdOPO (not shown), etc., to receive pulsed laser light from the laserengine 1200 and to generate OPO output pulses for application to aspecific target tissue type. The selector may be provided as part of auser interface, previously noted. In other embodiments, the OPO selectormay enable a user to select one of the first OPO 1240, second OPO, thirdOPO, etc., to receive pulsed laser light from one of the laser engine1200, the SHG, and another of the first OPO 1240, the second OPO, thethird OPO, etc., to generate additional desired wavelength(s) to treatdifferent types of target tissue.

Referring again to FIG. 12, in some embodiments the dermatological lasertreatment system 1200 may comprise a second harmonic generator (SHG)1230. The SHG 1230 may be similar to SHG 630 discussed in connectionwith FIG. 6, and receives the laser pulses from the laser engine 1220and generates second harmonic laser pulses with a wavelength that ishalf that of the pulses received from the laser engine 1220. Manydifferent crystals, such as potassium titanyl phosphate (KTP), lithiumtetraborate (LBO), and potassium dihydrogen phosphate (KDP) may be usedto generate the second harmonic of the first wavelength of the pulsesfrom the laser engine 1220, depending upon the first frequency and othersystem needs.

In embodiments incorporating a SHG 1230, the dermatological lasertreatment system 1200 may be capable of delivering, via applicator 1250,multiple wavelengths of treatment light to the target tissue. In thesingle-OPO system 1200 of FIG. 12, the user may select (e.g., using oneor more optical multiplexers 1265, 1275, 1285), optical pulses forapplication to the skin of a patient using the applicator 1250. Thepulses may be selected to have one of a first wavelength output from thelaser engine 1220 (along output path 1270, 1260, 1330, 1290); one ormore second wavelengths (e.g., an OPO signal wavelength or OPO idlerwavelength) from the OPO 1240 (along output path 1280, 1290); a thirdwavelength output from the SHG 1230 as the second harmonic of the firstwavelength (along path 1320, 1330, 1290), and a one or more for fourthwavelengths that are output from the OPO 1240 when pumped by the SHG1230 output pulses instead of the laser engine 1220 output pulses (alongpath 1320, 1300, 1280, 1290. Where multiple OPOs are used (not shown) itwill be appreciated that a still greater number of selectable wavelengthoptions will be available to a user to treat a target tissue.

Referring again to FIG. 12, additional details of some laser engine 1220embodiments are provided. Laser diode 1202 is adapted to output pulsedlaser light having a selected laser diode wavelength, which may beselected for optimally pumping microlaser 1204. In one embodiment, thelaser diode wavelength is in the range of 808-880 nm, and the laserdiode has sufficient peak power that the pulse repetition rate of themicrolaser 1204 is greater than 100 Hz and more preferably greater than1000 Hz. Microlaser 1204 is adapted to receive the pulsed laser lightoutput from the laser diode 1202 and to output pulsed laser light havingthe first wavelength of from 500-1200 nm, a pulse width (PW) of 10 psecto 10 nsec, and a first pulse energy (PE) of 100 mJ/pulse to 5 J/pulse.In one embodiment, the microlaser includes an input coupler 1206comprising a mirror having a high transmission at the selected laserdiode wavelength and a high reflectance at the first wavelength, anonlinear crystal 1208 (e.g., Nd:YAG) having a length of 2-10 mm, and asaturable absorber 1210 (i.e., a Cr⁴⁺:YAG crystal acting as a Q-switch)with an unsaturated transmission between 5 and 40%. In preferredembodiments, the saturable absorber 1210 is monolithically bonded to thenonlinear crystal 1208. The microlaser 1204 also includes an outputcoupler 1212 having a transmission of the first wavelength of from about25-75%, and at least 10% greater transmission on the orthogonal,non-lasing polarization. In one embodiment, the output coupler 1212 maycomprise a grating waveguide mirror. Laser engine 1220 also includes alaser amplifier 1214 to amplify the output pulses from the microlaser1204. In one embodiment laser amplifier 1214 is a multi-stage amplifiercomprising laser diode or flashlamp pumped Nd:YAG laser rods such thatthe total stored energy for 200 msec of pumping exceeds 10 J, andpreferably greater than 20 J. In such an embodiment, the output of thelaser amplifier 1214 comprises 200 msec bursts of 1064 nm, picosecondduration pulses with a frequency (or repetition rate) defined by themicrolaser. Notwithstanding the foregoing specific examples of amplifierdesigns, it will be appreciated that other amplifier designs may be usedand are considered within the scope of the present disclosure.

As noted, in some embodiments the dermatological laser treatment system1200 may provide therapy pulses in one or both of a pulse mode and aburst mode. The figures herein illustrate OPO designs that may be usedin certain embodiments of OPO 1240, whether operating in pulse mode orburst mode (FIG. 11). In the following discussion, numbers 800-860 referto structures in an OPO design according to FIG. 8, while numbers1100-1160 refer to structures in an OPO design according to a burst modeof operation in FIG. 11. In particular, an OPO 800, 1100 may be used asan OPO 1240 in dermatological laser treatment systems 1200 (FIG. 12).The OPO 800, 1100 includes an input coupler 820, 1120 for receivinginput pulses from a laser engine (e.g., laser engine 1220) having afirst wavelength. In one embodiment, the input pulses have a pulse widthof 10 psec-100 nsec and a first wavelength. The input coupler 820, 1120comprises a mirror having a high transmission at the first wavelengthand a high reflectance at one of the OPO signal wavelength and the OPOidler wavelength.

OPO 800, 1100 also includes a resonant cavity including a nonlinearcrystal 830, 1130 that induces parametric amplification of the inputpulses to produce OPO signal pulses 850, 1150 and OPO idler pulses 860,1160 having a second wavelength. It will be appreciated that in FIG. 11the signal and idler pulses 1150, 1160 are pulses within a pulse burst,produced from a corresponding input burst (B) 1110 comprising aplurality of pulses separated by a short time interval. In differentembodiments, one of the signal or idler pulses is output from the OPO800, 1110 as OPO output pulses which may be provided to treat a targettissue type. In one embodiment, the OPO is designed and constructed suchthat the second wavelength is selected from a) a wavelength at whichsebum tissue has a higher absorption coefficient than water and b) awavelength at which collagen tissue has a higher absorption coefficientthan water. In one embodiment, the wavelength is within one of a firstrange of from 1700-1770 nm, a second range of from 2280-2360 nm, and athird range of 5900-9500 nm. In one embodiment, the nonlinear crystal830, 1130 has a crystal length of 5-40 mm and comprises one of betabarium borate (BBO), lithium niobate (LiNbO3), potassium titanylearsenate (KTA), potassium titanium oxide phosphate (KTP) and zincgermanium phosphide (ZGP).

Finally, OPO 800, 1100 includes an output coupler 840, 1140 comprising amirror having a high reflectance at the first wavelength andtransmitting a selected portion of the second wavelength. The outputcoupler 840, 1140 may be constructed to achieve a desired transmissionof the second wavelength from, e.g., 10-99%, preferably 25-75%, morepreferably 40-60%.

OPOs 800, 1100 may be part of an OPO system that may include anadjustment element operable by a user to adjust the second (output)wavelength of the OPO output pulses (e.g., the OPO signal or idlerwavelength, depending upon the OPO design). The adjustment element maycomprise one or both of a) a crystal angle positioner coupled to thenonlinear crystal, wherein the crystal angle positioner is capable ofvarying the angle of incidence of the nonlinear crystal to the beam axisof the OPO input pulses to adjust the second wavelength and b) atemperature selector to adjust the temperature of the nonlinear crystalto a desired temperature.

In one embodiment, the OPO output pulses may comprise the OPO signalpulses, and the OPO signal pulse wavelength may be selected tocorrespond to an OPO idler wavelength for which a portion of the energyof the idler pulses is at least partially absorbed by the nonlinearcrystal.

In a specific example, continuing the 1064 nm laser engine outputexample described in connection with the laser amplifier 1214, the 1064bursts may be used to directly pump an OPO 1240, or may be used to pumpan LBO (lithium triborate) or KTP SHG crystal to produce 532 nm emissionwhich is then used to pump the OPO. In one embodiment, OPO 1240 outputpulses or bursts of 1726 nm laser light may be generated by couplingoutput bursts of 532 nm, 750 psec pulses, using input coupler 1120, intoa BBO (barium borate) nonlinear crystal 1130 laser cavity having alength of 5-20 mm that is oriented or positioned to produce OPO signaland idler wavelengths of 769 nm and 1726 nm, respectively. Input coupler1120 is designed for high transmission at 532 nm, and high reflection at769 and 1726 nm. Output coupler 1140 is designed to by high reflectanceat 769 nm and partially reflective (e.g., 50-75%) at 1726 nm.

In a second example, a 1064 nm, 200 msec burst of 750 psec pulses fromlaser engine 1220 is coupled through input coupler 1120 into a BBO orLiNbO3 nonlinear crystal 1130 that is oriented to produce OPO signal andidler wavelengths of 1726 nm and 2774 nm, respectively. The inputcoupler 1120 is designed for high transmission at 1064 nm and highreflection at 1726 and 2774 nm, while output coupler 1140 is designed tobe high reflectance at 2774 nm and partially reflective (e.g., 50-75%)at 1726 nm.

In another embodiment, the foregoing OPO could also be tuned byadjusting the crystal angle by approximately 1 degree to produce signaland idler wavelengths of 1550 and 3394 nm, respectively. In furtherembodiments, the foregoing OPO could be tuned by adjusting the crystalangle to produce signal and idler wavelengths of 1667 and 2940 nm,respectively, or to produce signal and idler wavelengths of 1927 and2376 nm, respectively. Wavelengths of 1550 and 2940 nm are frequentlyused for non-ablative and ablative skin resurfacing. Laser emission at1927 nm is used for skin resurfacing and also for treating pigmentedlesions. These applications require laser exposure times between 0.5 to100 msec which can again be achieved by burst mode operation of thelaser source. As shown by these examples, the OPO laser in systemsdisclosed herein can be act as a tunable light source to target multipleapplications including acne, wrinkles, scars, melisma, dyschromia,tattoos, actinic keratosis, and pigmented lesions.

As another example, multiple OPOs may be used in series to producewavelengths to target collagen in the 6000 nm region. For example, the1064 nm microlaser 1204 with laser amplifier 1214 described above can beused to pump an OPO 1240 using two KTP crystals to generate OPO outputpulses around 2000 um from a first OPO 1240. This emission can then beused to pump a second OPO (not shown) using a ZGP nonlinear crystal 1130that may be adjusted (or tuned) to produce emission of from 6000 to10,000 nm from 6 to 10 um by adjusting the crystal angle of the first orsecond OPO. Skin resurfacing may be done using a fractionated array oflaser spots, where the exposure duration at each spot is in the range of0.5 to 100 msec to limit thermally damaging adjacent tissue. This canagain be achieved by burst mode operation of the laser source.

In various embodiments, the present invention relates to the subjectmatter of the following numbered paragraphs.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. Embodiments of the present invention disclosed andclaimed herein may be made and executed without undue experimentationwith the benefit of the present disclosure. While the invention has beendescribed in terms of particular embodiments, it will be apparent tothose of skill in the art that variations may be applied to systems andapparatus described herein without departing from the concept, spiritand scope of the invention. Examples are all intended to benon-limiting. It is therefore evident that the particular embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the invention, which arelimited only by the scope of the claims.

What is claimed is:
 1. A dermatological treatment system for treating aplurality of skin conditions using pulsed laser light having a selectedwavelength, comprising: a laser engine adapted to output pulsed laserlight having a first wavelength of from 500-1200 nm, a pulse width of 10psec to 10 nsec, and a first pulse energy of from 100 mJ/pulse to 5J/pulse; and at least one optical parametric oscillator (OPO) adapted toreceive pulsed laser light from the laser engine and to generate OPOoutput pulses having a second wavelength selected from a wavelength atwhich sebum tissue has a higher absorption coefficient than water and awavelength at which collagen tissue has a higher absorption coefficientthan water, wherein the OPO output pulses comprise one of OPO signalpulses and OPO idler pulses; and an applicator adapted to receive andapply a selected one of the pulsed laser light output from the laserengine and the OPO output pulses to a target body tissue comprisingsebum tissue, collagen tissue, and a third tissue that is neither sebumnor collagen.
 2. The dermatological treatment system of claim 1, whereinthe laser engine is adapted to operate in one of a first treatment modeand a second treatment mode, wherein in the first treatment mode thelaser engine outputs laser pulses at a pulse frequency of from 0.1 Hz to100 Hz; and wherein in the second treatment mode the laser engineoutputs laser bursts at a burst frequency of 1 Hz to 100 Hz, each laserburst having a burst duration of from 500 μsec to 50 msec, a burstenergy of from 10 mJ to 20 J, and comprising a plurality of laser pulseshaving a pulse frequency greater than 100 Hz; the system furthercomprising a laser engine controller for controlling the operation ofthe laser engine in the first treatment mode and the second treatmentmode.
 3. The dermatological treatment system of claim 2, furthercomprising a user interface coupled to the laser engine controller,wherein the user interface allows a user to select one of the firsttreatment mode and the second treatment mode, and to control at leastone of the pulse frequency and the burst frequency.
 4. Thedermatological treatment system of claim 1, wherein the at least one OPOcomprises: a first OPO adapted to receive pulsed laser light from thelaser engine and to generate OPO output pulses having a secondwavelength at which sebum tissue has a higher absorption coefficientthan water, and a second OPO adapted to receive pulsed laser light fromthe laser engine and to generate OPO output pulses having a thirdwavelength at which collagen tissue has a higher absorption coefficientthan water.
 5. The dermatological system of claim 4, further comprisinga third OPO adapted to receive pulsed laser light from the laser engineand to generate OPO output pulses having a fourth wavelength that is awavelength at which water has a higher absorption coefficient than sebumtissue and collagen tissue.
 6. The dermatological system of claim 5,further comprising an OPO selector allowing a user to select one of thefirst OPO, the second OPO, and the third OPO to receive pulsed laserlight from the laser engine.
 7. The dermatological system of claim 5,wherein the second wavelength is a wavelength within one of a firstrange of from 1700-1770 nm and a second range of from 2280-2360 nm; thethird wavelength is a wavelength within a third range of 5900-9500 nmthe fourth wavelength is a wavelength within one of a fourth range offrom 1400-1850 nm, a fifth range of from 1910-1950 nm, and a sixth rangeof from 2600-3500 nm.
 8. The dermatological system of claim 7, whereinthe second wavelength is one of about 1726 nm and about 2300 nm, andwherein the third wavelength is one of about 6049 nm and about 6476 nm.9. The dermatological treatment system of claim 1, wherein the firstwavelength is a wavelength within the range of from 1000-1200 nm, thesystem further comprising: a second harmonic generator (SHG) adapted toreceive the pulsed laser light output from the laser engine and tooutput pulsed laser light having an SHG output wavelength that is halfthe first wavelength; and an OPO input selector allowing a user toselect one of the pulsed laser light output from the laser engine andthe pulsed laser light output from the SHG as the input to the OPO. 10.The dermatological treatment system of claim 9, wherein the OPO inputselector comprises at least one optical multiplexer adapted to directthe pulsed laser light output from the laser engine to a selected one ofthe at least one OPO and the SHG, wherein the user can select an OPOinput wavelength by directing laser pulses from one of the laser engineand the SHG as the input to the at least one OPO.
 11. The dermatologicaltreatment system of claim 9, further comprising: a user-selectable firstoutput path located between the laser engine and the SHG, wherein theuser may select the first output path to output first laser pulses tothe applicator; a user-selectable second output path located between theSHG and the OPO, wherein the user may select the second output path tooutput second harmonic laser pulses to the applicator; and auser-selectable third output path located proximate the OPO signaloutput, wherein the user may select the third output path to output OPOsignal pulses to the applicator.
 12. The dermatological treatment systemof claim 1, further comprising an applicator input selector comprisingat least one optical multiplexer allowing a user to direct a selectedone of pulsed laser light output from the laser engine and OPO outputpulses to the applicator for application to the target body tissue ofthe patient.
 13. The dermatological treatment system of claim 1, whereinthe laser engine comprises one of: a) a laser engine comprising: a laserdiode adapted to output pulsed laser light having a selected wavelength;a microlaser adapted to receive the pulsed laser light output from thelaser diode and to output pulsed laser light having the firstwavelength, the first pulse width, and a microlaser pulse energy of fromof from 10 μJ/pulse to 5 mJ/pulse; and an amplifier adapted to receivethe pulsed laser light output from the microlaser and to outputamplified laser pulses having the first wavelength, the first pulsewidth, and the first pulse energy; and b) a hybrid modelocked laser. 14.The dermatological treatment system of claim 1, wherein each of the atleast one OPOs comprises: a resonant cavity including a nonlinearcrystal comprising one of beta barium borate (BBO), lithium niobate(LiNbO3), potassium titanyle arsenate (KTA), potassium titanium oxidephosphate (KTP) and zinc germanium phosphide (ZGP); a first mirrorcoupled to a first end of the resonant cavity; a second mirror coupledto a second end of the resonant cavity; and an adjustment elementoperable by a user to adjust the second wavelength of the OPO outputpulses.
 15. The dermatological treatment system of claim 1, furthercomprising an adjustment element operable by a user to adjust the secondwavelength of the OPO output pulses, wherein the adjustment elementcomprises at least one of: a crystal angle positioner coupled to thenonlinear crystal, wherein the crystal angle positioner is capable ofvarying the angle of incidence of the nonlinear crystal to the beam axisof the OPO input pulses to adjust the second wavelength; and atemperature selector stabilizer to adjust the temperature of thenonlinear crystal to a desired temperature.
 16. The dermatologicaltreatment system of claim 1, wherein the applicator comprises ahandpiece constructed and arranged to be held in the hand of a user. 17.The dermatological treatment system of claim 1, the system furthercomprising a housing within which the laser engine is located, whereinone of the at least one OPOs is located in one of the applicator and thehousing.
 18. The dermatological treatment system of claim 17, furthercomprising an articulated arm having a proximal end coupled to thehousing and a distal end coupled to the applicator, wherein a user mayselect one of pulsed laser light output from the laser engine and OPOoutput pulses to be applied to the target tissue through an opticalmedium located in the articulated arm.
 19. The dermatological treatmentsystem of claim 1, wherein the laser engine comprises a laser diodeadapted to output pulsed laser light having a selected laser diodewavelength; a microlaser adapted to output pulsed laser light at thefirst wavelength, the microlaser comprising: an input coupler comprisinga mirror having a high transmission at the selected laser diodewavelength and a high reflectance at the first wavelength; a nonlinearNd:YAG crystal having a length of 2-10 mm; a saturable absorbercomprising a Cr⁴⁺:YAG crystal with an unsaturated transmission between 5and 40%, wherein the saturable absorber is monolithically bonded to thenonlinear Nd:YAG crystal; and an output coupler having a transmission ofthe first wavelength of from about 25% to about 75%; and a multi-stageamplifier comprising a Nd:YAG crystal to amplify the pulsed laser lightoutput from the microlaser.
 20. An optical parametric oscillator (OPO)system for use in a dermatological laser treatment system, the OPOsystem comprising: an input coupler for receiving laser input pulseshaving a pulse width of from 10 psec to 100 nsec and a first wavelength,the input coupler comprising a mirror having a high transmission (HT) atthe first wavelength and a high reflectance (HR) at one of an OPO signalwavelength and an OPO idler wavelength; a resonant cavity including anonlinear crystal having a crystal length between 5 and 40 mm, whereinthe resonant cavity produces OPO output pulses in response to receivingthe laser input pulses, the OPO output pulses having a second wavelengthselected from a wavelength at which sebum tissue has a higher absorptioncoefficient than water and a wavelength at which collagen tissue has ahigher absorption coefficient than water, wherein the OPO output pulsescomprise one of OPO signal pulses and OPO idler pulses; and an outputcoupler comprising a mirror having a high reflectance (HR) at the firstwavelength and transmitting a selected portion of the second wavelength.21. The OPO system of claim 20, wherein the nonlinear crystal comprisesone of beta barium borate (BBO), lithium niobate (LiNbO3), potassiumtitanyle arsenate (KTA), potassium titanium oxide phosphate (KTP) andzinc germanium phosphide (ZGP).
 22. The OPO system of claim 20, whereinthe second wavelength the second wavelength is a wavelength within oneof a first range of from 1700-1770 nm, a second range of from 2280-2360nm, and a third range of 5900-9500 nm.
 23. The OPO system of claim 20,wherein the second wavelength is selected from one of about 1726 nm,about 2305 nm, about 6049 nm, and about 6476 nm.
 24. The OPO system ofclaim 20, further comprising an adjustment element operable by a user toadjust the second wavelength of the OPO output pulses, wherein theadjustment element comprises at least one of: a crystal angle positionercoupled to the nonlinear crystal, wherein the crystal angle positioneris capable of varying the angle of incidence of the nonlinear crystal tothe beam axis of the OPO input pulses to adjust the second wavelength;and a temperature selector stabilizer to adjust the temperature of thenonlinear crystal to a desired temperature.
 25. The OPO system of claim20, wherein the OPO output pulses comprise OPO signal pulses, and theOPO signal pulses have a wavelength selected to correspond to an OPOidler wavelength for which a portion of the energy of the idler pulsesis at least partially absorbed by the nonlinear crystal.